1. Technical Field
The present disclosure relates to cryogenic storage systems. More particularly, the present disclosure relates to a system for maintaining a variable but isothermal temperature in a cryogenic storage system.
2. Background of Related Art
Maintenance of material in a cryogenic storage system at low temperature is typically limited to specific temperature ranges associated with the properties of the particular cryogenic fluid used in the cryogenic storage system, e.g., about 77° K. for liquid nitrogen at a pressure of 1 atmosphere. If mechanical cryogenic refrigeration equipment is used, the properties of the selected refrigerant or cryogen govern the nominal operating temperature of the system, so selection of a particular temperature is again limited to the cryogens available having the temperature characteristics. Regardless of the refrigeration method selected, mechanical cryogenic refrigeration or bulk liquid cryogen, operation at a particular cryogenic temperature requires a different approach. Since both mechanical cryogenic refrigeration and bulk liquid cryogen refrigeration are limited in their temperature ranges, a need exists for maintaining a biological material in a cryogenic storage system.
A preferred refrigeration choice is the use of a saturated cryogen, in small quantities, which nominally produces stable and economical refrigeration for long periods in standard cryogenic Dewars.
An object of the present disclosure is to use a cryogen or refrigerant to maintain an isothermal volume at a stable temperature.
Another object of present disclosure is to allow the selection of a discrete temperature range for any given cryogen.
Yet another object of the present disclosure is to allow discrete temperature control within the selected temperature range.